The present invention relates to a process for the removal of ink from printed wastepaper in the course of reclaiming the fiber content of the waste for reuse in the manufacture of new paper. More particularly, the present invention relates to an improvement in the wastepaper deinking process, provided by a specific class of surface active deinking agents.
Wastepaper has long served as a source of the raw fiber materials used in papermaking. Traditionally, fiber from wastepaper was utilized only in the production of low grade paper and paperboard products. Today, however, greater utilization of reclaimed fiber (about 25 percent of the total fiber used in papermaking) has provided incentive for taking steps to upgrade the reclaimed product. These steps include treatment to effectively remove ink from waste fibers in order to permit their use in the manufacture of high quality papers.
In the course of the conventional paper reclamation process of interest, deinking procedures include steps for converting the wastepaper to pulp and contacting the pulp with a alkaline aqueous deinking medium containing a chemical deinking agent. The physical pulping and the alkalinity of the aqueous medium cause the removal of ink from the pulp fiber and the deinking agent produces a suspension, (and/or dispersion) of the ink particles thus removed in the aqueous medium. The resulting mixture is subsequently treated to separate the suspended ink from the pulp.
The present invention centers on the use in such a deinking process of a chemical deinking agent which is an ethylene oxide adduct of a detergent-range (e.g., C.sub.9 to C.sub.18) thiol. It has been known in the paper deinking art (for example, U.S. Pat. No. 4,162,186) to employ chemical agents which are ethylene oxide adducts ("ethoxylates") of detergent-range alcohols or alkyl-substituted phenols. Although these alcohol and phenol derivatives have generally proved acceptable for use in this service, a deinking agent which is more cost-effective in its performance would be highly desirable. Moreover, the use of alcohol or alkylphenol ethoxylates suffers some disadvantage when consideration is given to all aspects of the typical deinking process. For instance, the presence of conventional surface active deinking agents in deinked pulp and other process streams may interfere with downstream processing steps and/or the quality of effluent wastewater.